Measurements and ecological implications of non‐rainfall water in desert ecosystems—A review

Abstract

The current review focuses on the contribution of non-rainfall water (NRW) to arid and semiarid regions (with a focus on the Negev), where NRW may provide a constant source of water that may facilitate the survival of different organisms, especially microorganisms. Factors that determine the amounts of NRW and the contribution of NRW to plants and organisms are discussed. Nevertheless, although important, significant variation exists regarding the amounts of NRW, which may stem from improper use or inherent drawbacks of some of the measurement devices. This may lead to erroneous conclusions regarding the possible role played by NRW. For instance, with prokaryotes (bacteria and cyanobacteria) requiring liquid water (≥0.1 mm) for growth, small inaccuracies in NRW around this threshold may either lead to the conclusion that NRW is sufficiently high to facilitate their growth, or rather, is too low to facilitate their growth. Arguing that some of the devices used to measure NRW may greatly overestimate the amounts, the possible contribution of NRW to soil bacteria and cyanobacterial biocrusts is analysed. We suggest that although NRW may assist the growth and survival of mosses and some types of lichens (mostly non-crustose), no conclusive findings were thus far reported regarding the use of dew for cyanobacteria growth. The use of dew by cyanobacterial crust for growth should be critically examined, and the possibility that NRW may even result in a negative carbon balance for cyanobacterial crusts should be considered.

Are coastal deserts necessarily dew deserts? An example from the Tabernas Desert

“…Likewise, we are also inclined to suggest that the lush cover of soil lichens in the Tabernas is at least partially linked to the higher amounts and frequent occurrence of rain events and subsequently to the possible use of rainwater by these soil lichens (Lázaro, 2004). On the other hand, the low cover of soil lichens in the Negev cannot be linked to the frequent occurrence of dew but rather to the low amounts of rain (Kidron and Starinsky, 2019). This may explain the confinement of lichens to the feet of rock outcrops where they benefit from extra water by runoff (Fig.…”

Assessing the likelihood of the soil surface to condense vapour: The Negev experience

“…Highlands: limestone hills with loessial wadis (a), lithobionts (lichens) covering the bedrocks while cyanobacterial crusts (with lichens confined to the feet of the bedrocks) covering the loessial soil (b), lithoibionts (epilithic and endolithic lichens) covering cobbles (c), measurements of the nonrainfall water (NRW) at the soil surface, at the cobbles and the glass plates, CPM (d), and measurements of temperatures on the cobble, the soil surface, and in the air, at 10-cm height above ground (e) (1970b) also applies to other Negev lichens. An amount of 0.05 mm was found necessary to facilitate net photosynthesis of R. maciformis (Kidron & Starinsky, 2019). This is half the amount necessary for vapour condensation (0.1 mm; Lange et al, 1992), which also marks the threshold between a visibly wet and a dry surface (Kidron, Herrnstadt, & Barzilay, 2002).…”

“…By adjacently attaching identical‐size pieces of cloths and R. maciformis thalli to different rock and cobble surfaces, calibration between NRW adsorbed by the cloths and thalli allowed to determine the threshold amount of water necessary to reactivate the photosynthetic apparatus of R. maciformis , which according to Lange et al () also applies to other Negev lichens. An amount of 0.05 mm was found necessary to facilitate net photosynthesis of R. maciformis (Kidron & Starinsky, ). This is half the amount necessary for vapour condensation (0.1 mm; Lange et al, ), which also marks the threshold between a visibly wet and a dry surface (Kidron, Herrnstadt, & Barzilay, ).…”

“…Many of the devices do not reflect the intact soil, requiring detailed calibration. As lately discussed by Kidron and Starinsky (2019), this is not commonly done. Even measuring the NRW with MLs entails substantial difficulties that may result in erroneous interpretations (Kidron & Kronenfeld, 2017).…”

Variations in dew moisture regimes in desert ecosystems and their influencing factors

“…, and biological soil crusts (Jia et al, 2014;Kidron & Starinsky, 2019;Lange, Geiger, & Schulze, 1977;Pan, Wang, Zhang, & Hu, 2018;Prado & Sancho, 2007;Rao et al, 2009;Sun et al, 2008;Tao & Zhang, 2012;Temina & Kidron, 2015;Xiao et al, 2019;Zhang et al, 2009) are mainly from non-rainfall water inputs, such as fog, dew, and water vapor adsorption (Kaseke et al, 2012;, which are three main mechanisms of adding moisture to the uppermost soil surfaces of the different types of deserts ( Figure 1).…”